It is conventional during the manufacture of an alternator to form the slip rings directly on a projecting part of the alternator shaft.
Another known technique consists in making the slip ring unit, or collector, as a separate component, using for example a method whereby the body of the component is moulded on to its electrically conductive parts. The slip ring unit is subsequently fitted on to the shaft of the alternator, typically by force fitting.
Such a slip ring unit, formed in the known way as a separate component, comprises a generally cylindrical first body portion which includes two slip rings at its outer surface, together with electrical connecting elements for connecting the slip rings with the ends of wires of a winding of the alternator.
It is also known to provide such a slip ring unit or collector which includes, on the side of the body (i.e. at the end of the slip ring unit) on which the fitting force is to be applied, an extension of the insulating material which extends over a short axial distance, so as to provide satisfactory location of the adjacent slip ring in the axial direction. Thus, when the slip ring unit is being fitted on to the alternator shaft, the applied force is exerted on this extension of the insulating material. Since the applied force is necessarily large, there is a substantial danger of damage or fracture of the insulating material in this region, which is of course highly undesirable.
A first object of the present invention is to overcome this drawback.
In addition, in cases where the separate slip ring unit has a symmetry of revolution over 180.degree., with, in particular, two diametrically opposed wire end connecting elements, the orientation of the slip ring unit in one or other of the two possible angular positions does not, in general, matter. However, this orientation determines which end, i.e. the outer end or the inner end, of the excitation winding of the alternator will be connected to which slip ring (outer or inner) of the alternator. It has been found, unexpectedly, that the two possible ways of making this connection affect in different ways the behavior of the alternator as regards electromagnetic perturbations, especially in radio frequency wavebands.